374 SEA-SIDE STUDIES. 



examination, tlie facts required by the doctrines were not 

 discoverable, but, in lieu thereof, facts altogether opposed 

 to them. 



A passage from Professor Sharpey, one of the latest, and 

 assuredly one of the best anatomical authorities, will present 

 the views held on this subject. " When subjected to the 

 microscope, the nervous substance is seen to consist of two 

 different structural elements — viz. fibres and cells or vesicles. 

 The fibres are found universally in the nervous chords, and 

 they also constitute the greater part of the nervous centres ; 

 the cells or vesicles, on the other hand, are confined, in a 

 great measure, to the cerebro-spinal centre and the ganglia, 

 and do not exist in the nerves properly so called, unless it 

 be at their peripheral expansions in some of the organs of 

 special sense." * According to my observations, the fore- 

 going statements are contradicted on the following points : 

 1st, Nervous chords exist in abundance absolutely luithout 

 fibres. 2d, The nervous centres of some vertebrates are 

 without fibres. 3d, Cells do exist in the nerves. 



The physiologist will read with surprise of the absence of 

 fibres in the nerves, which are universally held to be simply 

 fasciculi of fibres ; and, indeed, the discovery so much sur- 

 prised me at first, that it was long before I could persuade 

 myself it was no optical illusion, or the result of disintegra- 

 tion in the nerve itself ; but having examined both fresh and 

 prepared specimens, in great quantities, I affirm, tliat in the 

 genera Doris, Pleurobranchus, Aplysia, Solen, and Limaa;, 

 the nerves are for the most part totally destitute of fibres. 



* SHABrEY and Ellis's edition of Quai/is Anatonii/, 1856 ; vol. i., p. clxxii. 



